Characterization and sexual dimorphic expression of Cytochrome P450 genes in the hypothalamic-pituitary-gonad axis of yellow catfish

Transcriptome analysis of four types of gonadal tissues in largemouth bass (Micropterus salmoides) to reveal its sex-related genes

The sex determination system of largemouth bass (Micropterus salmoides, LMB) is XX/XY; however, the underlying molecular mechanisms involved in early sex differentiation, gonadal development, and exogenous hormone-induced sex reversal remain unknown. In this study, LMB at 15 days post-hatching (dph) were fed diets containing 20 mg/kg of 17α-methyltestosterone (17α-MT) or 30 mg/kg of 17β-estradiol (17β-E2) for 60 days, respectively. Serum steroid levels, histological observations of the gonads, and identification of sex-specific markers were employed to screen the gonads of 60-day-old normal female fish (XX-F), normal male fish (XY-M), 17β-E2 induced pseudo-female fish (XY-F), and 17α-MT-induced pseudo-male fish (XX-M) for transcriptome sequencing in order to uncover genes and pathway involved in the process of sexual reversal. The results from histology and serum sex steroid hormone analysis showed that both 17α-MT and 17β-E2 were capable of inducing sex reversal of LMB at 15 dph. Transcriptome results revealed a total of 2,753 genes exhibiting differential expression, and the expression pattern of these genes in the gonads of XX-M or XY-F resembled that of normal females or males. The male sex-biased genes that are upregulated in XX-M and downregulated in XY-F are referred to as key genes for male reversal, while the female sex-biased genes that are upregulated in XY-F and downregulated in XX-M are referred to as key genes for female reversal. Finally, 12 differentially expressed genes (DEGs) related to male sex reversal were screened, including star2, cyp17a, cyp11b1, dmrt1, amh, sox9a, katnal1, spata4, spata6l, spata7, spata18 and foxl3. 2 DEGs (foxl2a and cyp19a1b) were found to be associated with female sex reversal. The changes in these genes collectively influence the direction of sex differentiation of LMB. Among them, star2, dmrt1 and cyp19a1b with significantly altered expression levels may play potentially crucial role in the process of gender reversal. The expression patterns of 21 randomly selected genes were verified using qRT-PCR which confirmed the reliability and accuracy of the RNA-seq results. These findings not only enhance our understanding of the molecular basis underlying sex reversal but also provide crucial data support for future breeding research on unisexual LMB.

Hypoxia-Inducible Factor 1α Affects Yak Oocyte Maturation and Early Embryonic Development by Regulating Autophagy

In animal assisted reproductive technology, the production of high-quality oocytes is crucial. The yak, having lived in the Qinghai-Tibet Plateau for an extended period, has reproductive cells that are regulated by hypoxia-inducible factor 1α (HIF-1α). This study aimed to investigate the impact of HIF-1α on yak oocyte maturation and early embryonic development in vitro through the regulation of autophagy. The in vitro maturation process of yak oocytes involved the addition of the HIF-1α inducer DFOM and the inhibitor LW6 to examine their effects on yak oocyte maturation, early embryonic development, cell autophagy, cytochrome P450s (CYP450s) enzyme expression, and cumulus diffusion factors. The findings revealed that DFOM significantly upregulated the expression of HIF-1α, resulting in increased the cumulus diffusion area, elevated first polar body expulsion rate of oocytes, enhanced mitochondrial and actin levels, decreased ROS production, and reduced early apoptosis levels of oocytes. Moreover, DFOM promoted the expression of autophagy-related proteins, CYP450s enzymes, and cumulus diffusion factors, thereby enhancing oocyte maturation and early embryonic development. Conversely, LW6 exhibited opposite effects. The inhibition of autophagy levels with 3-MA during DFOM treatment yielded similar outcomes. Furthermore, reducing autophagy led to increased apoptosis levels at all stages of early embryonic development, as well as a significant decrease in total cell number and ICM/TE ratio of blastocysts. Studies have shown that during the in vitro maturation of yak oocytes, HIF-1α can affect the cumulus expansion area of oocytes by regulating autophagy, the first polar body excretion rate, mitochondrial level, actin level, ROS and early apoptosis level, the CYP450s enzyme, and the expression of cumulus expansion factors, thereby improving the in vitro maturation and early embryonic development of yak oocytes. These findings offer valuable insights into the reproductive regulation mechanism of yaks in hypoxic environments and suggest potential strategies for the advancement of yak assisted reproductive technology.

Genome-wide analysis of the cytochrome P450 gene family in Pacific oyster Crassostrea gigas and their expression profiles during gonad development

The cytochrome P450 (CYP) gene superfamily plays a significant role in various physiological processes, producing different compounds such as hormones, fatty acids, and biomolecules. However, little information is known their roles during gonad development in Pacific oyster (Crassostrea gigas). In this study, total of 116 CgCYP (Crassostrea gigas cytochrome P450) genes were identified and their expression pattern was analyzed for the first time. The relative molecular weights of these CgCYP genes ranged from 63.52 to 113.41 kDa, and the length of encoded amino acids ranged from 103 to 993. And total 26 cis-acting elements of these CgCYP genes were identified. GO and KEGG enrichment analysis showed some CgCYP genes are essential for the metabolism of male and female sex hormones. Additionally, expression anslysis showed 69 CgCYP genes were over-expressed in early gonad development and triploid infertile individuals. More importantly, expression levels of CgCYP1, CgCYP15, CgCYP34, CgCYP46, CgCYP69, CgCYP87, CgCYP88, and CgCYP103, were found to be significantly higher in female gonad, suggesting their important roles in female gonad development. The results of this study will provide a better understanding of the CgCYP genes in the gonad development of Pacific oyster.

Gonadal Transcriptome Analysis Reveals that SOX17 and CYP26A1 are Involved in Sex Differentiation in the Chinese Soft-Shelled Turtle (Pelodiscus sinensis)

The Chinese soft-shelled turtle (Pelodiscus sinensis) is an important aquaculture animal in China and exhibits growth dimorphism. Single-male cultures are often selected for higher economic efficiency. However, the mechanism of sex differentiation in P. sinensis is not well-known. In this study, a comparative transcriptome analysis of male (ZZ)- and 17β-oestradiol (E2)-induced pseudo-female (ZZ + E2)-stage embryonic gonads of P. sinensis was performed. A total of 420 differentially expressed genes (DEGs), which included 271 upregulated genes and 149 downregulated genes, were identified. These DEGs were mainly involved in several sex-related pathways, such as "ovarian steroidogenesis", "steroid hormone biosynthesis", "PPAR signalling pathway", and "metabolism of xenobiotics by cytochrome P450". In addition, 50 known and novel candidate genes involved in sex differentiation, such as the male-biased genes AMH, DMRT1, TBX1, and CYP26A1 and the female-biased genes CYP1A1, RASD1, and SOX17, were investigated and identified. For further verification, the full-length cDNAs of SOX17 and CYP26A1 were obtained. SOX17 contains a 1218-bp ORF and encodes 405 amino acids containing an HMG functional domain unique to the Sox superfamily. CYP26A1 contains a 1485-bp ORF and encodes 494 amino acids. Different expression levels of SOX17 and CYP26A1 could be detected in all the tested tissues of males and females. Notably, the expression of CYP26A1 was markedly greater in the gonads of male embryos (P < 0.05) than in those of female embryos, whereas the expression of SOX17 showed the opposite trend (P < 0.05). Taken together, the RNA-seq and qRT‒PCR results suggested potential roles for SOX17 and CYP26A1 in promoting female and male gonadal development, respectively, in P. sinensis. Our results provide new evidence for the mechanism of sex differentiation in P. sinensis.

Interaction of 17α-ethinylestradiol and methyltestosterone in western mosquitofish (Gambusia affinis) across two generations

The interactions between estrogen and androgen in aquatic animals remain largely unknown. In this study, two generations (F0 and F1) of western mosquitofish (Gambusia affinis) were continuously exposed to 17α-ethinylestradiol (EE2, 10 ng/L), methyltestosterone (MT, 10 ng/L (MTL); 50 ng/L (MTH)), and mixtures (EE2+MTL and EE2+MTH). Various endpoints, including sex ratio (phenotypic and genetic), secondary sex characteristics, gonadal histology, and transcriptional profile of genes, were examined. The results showed that G. affinis exposed to MTH and EE2+MTH had a > 89.7 % of phenotypic males in F1 generation, with 34.5 and 50.0 % of these males originated from genetic females, respectively. Moreover, females from F0 and F1 generations exposed to MTH and EE2+MTH exhibited masculinized anal fins and skeletons. The combined effect of MT and EE2 on most endpoints was dependent on MT. Furthermore, significant transcriptional alterations in certain target genes were observed in both the F0 and F1 generations by EE2 and MT alone and by mixtures, showing some degree of interactions. These findings that the effects of EE2+MTH were primarily on the phenotypic sex of G. affinis in offspring generation suggest that G. affinis under chronic exposure to the binary mixture contaminated water could have sex-biased populations.

Comparative transcriptome profiles of four sexually size dimorphic fish

Sexual size dimorphism is widespread in fish species. Although sex growth differences in multiple species have been studied successively, the commonalities of regulatory mechanisms across sexually dimorphic species are unknown. In this study, we performed RNA-seq analysis of four representative fish (loach, half-smooth tongue sole, yellow catfish, and Nile tilapia) with significant growth differences between females and males. Clean reads were identified from four fish species, ranging from 45,718,052 to 57,733,120. Following comparison transcriptome analysis, there were 1,132 and 1,108, 1,290 and 1,102, 4,732 and 4,266, 748 and 192 differentially expressed genes (DEGs) in the brain and muscle of loach, half-smooth tongue sole, yellow catfish, and Nile tilapia, respectively. Furthermore, the expression levels were validated by quantitative real-time PCR (qRT-PCR). Comparative transcriptome profiles of four fish described here will provide fundamental information for further studies on the commonalities of sexually size dimorphic fish in regulating growth differences between females and males.

Sexually Dimorphic Gene Expression in X and Y Sperms Instructs Sexual Dimorphism of Embryonic Genome Activation in Yellow Catfish (Pelteobagrus fulvidraco)

Paternal factors play an important role in embryonic morphogenesis and contribute to sexual dimorphism in development. To assess the effect of paternal DNA on sexual dimorphism of embryonic genome activation, we compared X and Y sperm and different sexes of embryos before sex determination. Through transcriptome sequencing (RNA-seq) and whole-genome bisulfite sequencing (WGBS) of X and Y sperm, we found a big proportion of upregulated genes in Y sperm, supported by the observation that genome-wide DNA methylation level is slightly lower than in X sperm. Cytokine-cytokine receptor interaction, TGF-beta, and toll-like receptor pathways play important roles in spermatogenesis. Through whole-genome re-sequencing (WGRS) of parental fish and RNA-seq of five early embryonic stages, we found the low-blastocyst time point is a key to maternal transcriptome degradation and zygotic genome activation. Generally, sexual differences emerged from the bud stage. Moreover, through integrated analysis of paternal SNPs and gene expression, we evaluated the influence of paternal inheritance on sexual dimorphism of genome activation. Besides, we screened out gata6 and ddx5 as potential instructors for early sex determination and gonad development in yellow catfish. This work is meaningful for revealing the molecular mechanisms of sex determination and sexual dimorphism of fish species.

Tissue-Specific Expression Pattern in Ancherythroculter nigrocauda, a Sexually Size Dimorphic Fish

Certain members of the Actinopterygii class are known to exhibit sexual dimorphism (SD) that results in major phenotypic differences between male and female fishes of a species. One of the most common differences between the two sexes is in body weight, a factor with a high economic value in aquaculture. In this study, we used RNA sequencing (RNA-seq) to study the liver and brain transcriptomes of Ancherythroculter nigrocauda, a fish exhibiting SD. Females attain about fourfold body weight of males at sexual maturity. Sample clustering showed that both sexes were grouped well with their sex phenotypes. In addition, 2,395 and 457 differentially expressed genes (DEGs) were identified in the liver and brain tissues, respectively. The gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses predicted the association of PPAR signaling, cytochrome P450, and steroid hormone biosynthesis to the differences in sexual size. In addition, weighted gene co-expression network analyses (WGCNA) were conducted, and the green module was identified to be significantly correlated with sexual size dimorphism (SSD). Altogether, these results improve our understanding of the molecular mechanism underlying SSD in A. nigrocauda.

Molecular characterization and functional analysis of cyp11a and cyp11b in black rockfish (Sebastes schlegelii)

The cyp11 includes cyp11a and cyp11b in most mammals and teleosts, encoded cholesterol side chain lyase and 11β-hydroxylase, respectively. It is essential in steroid hormone synthesis. However, studies on the regulation of cyp11 are limited, especially in teleosts. In this study, the molecular characterization and function of cyp11a and cyp11b of black rockfish was investigated. Both of them showed high homology with other teleost counterparts by phylogenetic analysis. The expression of cyp11a and cyp11b exhibited a clear sexually dimorphic pattern, with a higher expression level in testis than that of in ovaries. During the different developmental stages (40 dpf, 80 dpf, 190 dpf, 360 dpf, 720 dpf), the expression of cyp11a was earlier than cyp11b. In situ hybridization results showed that cyp11a and cyp11b were mainly expressed in oogonia and oocytes of the ovary. They were located in spermatogonia and interstitial compartment in the 1.5-year-old gonads, and spermatocytesgonia and the peritubular myoid cell of the testis in the 2.5-year-old gonads. To explore the distinct roles of cyp11a and cyp11b in gonads, oestrogen and androgens were used to stimulate the primary testicular and ovarian cells. The expressions of cyp11a and cyp11b were tested under different dose of 17α-methyltestosterone (17α-MT) and 17β-estradiol (E2). The results showed cyp11a was significantly increased at 10^-6  mol ml^-1 of 17α-MT and 10^-8  mol ml^-1 of E2 in ovary and 10^-10  mol ml^-1 of 17α-MT and E2 in testis, while cyp11b was significantly decreased after 17α-MT and E2 treatment. These results indicated that cyp11a and cyp11b were likely to have different functions, and also implied they might play an important roles in the differentiation of gonads and the synthesis of steroids in black rockfish.

Synergistic Combination of Exogenous Hormones to Improve the Spawning and Post-spawning Survival of Female Yellow Catfish

Multiple repeat spawners make large contributions to long-term population stability and aquaculture breeding programs. A high percentage of female yellow catfish (Pelteobagrus fulvidraco) died for spawning failure or incomplete spawning after artificial spawning by traditional synthetic hormones including human chorionic gonadotropin (hCG), luteinizing hormone releasing hormone (LHRH), and domperidone (DOM). The present study was designed to compare the efficacy of different combinations of exogenous hormones for inducing ovulation in yellow catfish using hCG, LHRH, DOM, and carp pituitary extraction (CPE). We found a optimal strategy for exogenous hormones administration, the mixture of LHRH/CPE for the first injection and LHRH/CPE/DOM for the second injection, could greatly improve the rates of spawning success, weight of ovulated eggs and survival rate after spawning. Interestingly, a population of female yellow catfish with defective reproductive duct could not spawn and showed high mortality after induced by a combination of hCG/LHRH/DOM, whereas a synergistic combination of hCG, LHRH, DOM, and CPE could efficiently induce spawning and reduce mortality in the defective yellow catfish, in which a significant decrease of Vitellin and E2 levels. Altogether, our findings provide an effective combination of exogenous hormones to improve spawning and post-spawning survival of female yellow catfish.

Transcriptional Changes in the Ovaries of Perch from Chernobyl

Fish have been highly exposed to radiation in freshwater systems after the Chernobyl Nuclear Power Plant (NPP) accident in 1986 and in freshwater and marine systems after the more recent Fukushima NPP accident in 2011. In the years after the accident, the radioactivity levels rapidly declined due to radioactive decay and environmental processes, but chronic lower dose exposures persisted. To gain insights into the long-term effects of environmental low dose radiation on fish ovaries development, a high-throughput transcriptomic approach including a de novo assembly was applied to different gonad phenotypes of female perch: developed gonads from reference lakes, developed/irradiated from medium contaminated lake, and both developed/irradiated and undeveloped from more highly contaminated lakes. This is the most comprehensive analysis to date of the gene responses in wildlife reproductive system to radiation. Some gene responses that were modulated in irradiated gonads were found to be involved in biological processes including cell differentiation and proliferation (ggnb2, mod5, rergl), cytoskeleton organization (k1C18, mtpn), gonad development (nell2, tcp4), lipid metabolism (ldah, at11b, nltp), reproduction (cyb5, cyp17A, ovos), DNA damage repair (wdhd1, rad51, hus1), and epigenetic mechanisms (dmap1). Identification of these genes provides a better understanding of the underlying molecular mechanisms underpinning the development of the gonad phenotypes of wild perch and how fish may respond to chronic exposure to radiation in their natural environment, though causal attribution of gene responses remains unclear in the undeveloped gonads.

Gonadal Transcriptome Analysis of Sex-Related Genes in the Protandrous Yellowfin Seabream (Acanthopagrus latus)

Yellowfin seabream (Acanthopagrus latus), a protandrous hermaphroditic fish, is a good model for studying the mechanism of sex reversal. However, limited knowledge is known about the genetic information related to reproduction and sex differentiation in this species. Here, we performed de novo transcriptome sequencing analysis of the testis, ovotestis, and ovary to identify sex-related genes in yellowfin seabream. The results assembled 71,765 unigenes in which 16,126 and 17,560 unigenes were differentially expressed in the ovotestis and ovary compared to the testis, respectively. The most differentially expressed gene (DEG)-enriched Kyoto Encyclopedia of Genes and Genomes and GO pathways were closely associated with the synthesis of sex steroid hormones. Functional analyses identified 55 important sex-related DEGs, including 32 testis-biased DEGs (dmrt1, amh, and sox9, etc.), 20 ovary-biased DEGs (cyp19a, foxl2, and wnt4, etc.), and 3 ovotestis-biased DEGs (lhb, dmrt2, and foxh1). Furthermore, the testis-specific expression of dmrt1 and the brain-pituitary-ovary axis expression of foxl2 were characterized, suggesting that they might play important roles in sex differentiation in yellowfin seabream. Our present work provided an important molecular basis for elucidating the mechanisms underlying sexual transition and reproductional regulation in yellowfin seabream.

Roles of two cyp11 genes in sex hormone biosynthesis in Japanese flounder (Paralichthys olivaceus)

The P450 side-chain cleavage enzymes P450scc (Cyp11a) and 11β-hydroxylase (Cyp11b) play important roles in sex steroid and cortisol production. Here, two duplicates of cyp11 genes were identified in Japanese flounder (Paralichthys olivaceus): Pocyp11a and Pocyp11b, respectively. Phylogenetic analysis and amino acid sequence alignment revealed that Pocyp11a and Pocyp11b shared significant identity with sequences of other teleost fish species. The quantitative real-time polymerase chain reaction (qRT-PCR) results indicated that among the studied tissues, brain tissue showed the highest expression of Pocyp11a, followed by kidney and testis tissues, whereas Pocyp11b expression was highest in the testis. The expression patterns of these two genes showed sexual dimorphism, with both genes showing higher expression in the testis than in the ovary. In-situ hybridization analysis demonstrated that Pocyp11a and Pocyp11b mRNA were both detected in oocytes, spermatocytes, and Sertoli cells, indicating that they might be involved in hormone synthesis. The expression levels of Pocyp11a and Pocyp11b were significantly downregulated by treatment with 17α-methyltestosterone (17α-MT) in the testis and ovary in both in vivo and studies. In vivo studies showed that Pocyp11a and Pocyp11b transcripts were suppressed by 17β-estradiol (E₂ ) treatment in both the testis and ovary. In addition, in vitro studies showed that the expression level of Pocyp11b was decreased by treatment with E₂ , whereas that of Pocyp11a was largely unaffected. Moreover, the expression levels of Pocyp11a and Pocyp11b in the testis cell line were significantly upregulated after NR0b1 and NR5a2 (p < .05) treatment. These results indicate that Pocyp11a and Pocyp11b might play important roles in sex hormone biosynthesis. Our research can assist future studies of the mechanisms of steroid biosynthesis and functional differences between cyp11a and cyp11b in Japanese flounder.

Diverse and variable sex determination mechanisms in vertebrates

Sex is prevalent in nature and sex determination is one of the most fundamental biological processes, while the way of initiating female and male development exhibits remarkable diversity and variability across vertebrates. The knowledge on why and how sex determination mechanisms evolve unusual plasticity remains limited. Here, we summarize sex determination systems, master sex-determining genes and gene-regulatory networks among vertebrates. Recent research advancements on sex determination system transition are also introduced and discussed in some non-model animals with multiple sex determination mechanisms. This review will provide insights into the origin, transition and evolutionary adaption of different sex determination strategies in vertebrates, as well as clues for future perspectives in this field.

Characteristics of Cyp11a during Gonad Differentiation of the Olive Flounder Paralichthys olivaceus

The P450 side-chain cleavage enzyme, P450scc (Cyp11a) catalyzes the first enzymatic step for the synthesis of all steroid hormones in fish. To study its roles in gonads of the olive flounder Paralichthys olivaceus, an important maricultured fish species, we isolated the cyp11a genomic DNA sequence of 1396 bp, which consists of 5 exons and 4 introns. Semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) results indicated that the flounder cyp11a was exclusively expressed in gonad and head kidney tissues. Its expression level in the testis was higher than that in the ovary. According to the in situ hybridization patterns, cyp11a was mainly expressed in the Leydig cells of the testis, and the thecal cells of the ovary. Immunofluorescence analysis showed that Cyp11a was located in the cytoplasm of the cultured flounder testis cells. Further quantitative real-time PCR results presented the cyp11a differential expression patterns during gonad differentiation. Among different sampling points of the 17β-estradiol (E2, 5 ppm) treatment group, cyp11a expression levels were relatively high in the differentiating ovary (30 and 40 mm total length, TL), and then significantly decreased in the differentiated ovary (80, 100 and 120 mm TL, p < 0.05). The pregnenolone level also dropped in the differentiated ovary. In the high temperature treatment group (HT group, 28 ± 0.5 °C), the cyp11a expression level fluctuated remarkably in the differentiating testis (60 mm TL), and then decreased in the differentiated testis (80, 100 mm TL, p < 0.05). In the testosterone (T, 5 ppm) treatment group, the cyp11a was expressed highly in undifferentiated gonads and the differentiating testis, and then dropped in the differentiated testis. Moreover, the levels of cholesterol and pregnenolone of the differentiating testis in the HT and T groups increased. The expression level of cyp11a was significantly down-regulated after the cultured flounder testis cells were treated with 75 and 150 μM cyclic adenosine monophosphate (cAMP), respectively (p < 0.05), and significantly up-regulated after treatment with 300 μM cAMP (p < 0.05). Both nuclear receptors NR5a2 and NR0b1 could significantly up-regulate the cyp11a gene expression in a dosage dependent way in the testis cells detected by cell transfection analysis (p < 0.05). The above data provides evidence that cyp11a would be involved in the flounder gonad differentiation and development.

Stat5b Regulates Sexually Dimorphic Gene Expression in Zebrafish Liver

Sexual size dimorphism is an interesting phenomenon occurred in many fish species. Wildtype zebrafish exhibits a significant sexual dimorphism in body size at the adult stage. Previous studies indicated that sexual size dimorphism was eliminated in stat5b-mutated zebrafish. Herein, the comparative transcriptome analysis was conducted to observe the genes and pathways involved in sexual size dimorphism. The number of male-biased and female-biased genes was much less in the liver of stat5b mutant zebrafish than in wildtype. Gene ontology (GO) enrichment and Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis indicated that multiple pathways related to metabolism were affected upon loss of stat5b function. qRT-PCR results also validated that sexually dimorphic expression of a set of genes was lost when stat5b was mutated. Furthermore, the weighted correlation network analysis (WGCNA) detected many candidate genes related to the growth traits and stat5b function, such as greb1, lepr, and igf2b. Our data suggest that stat5b should regulate the sexually dimorphic gene expression in zebrafish liver and add in understanding of the molecular mechanisms underlying sexual size dimorphism in fish species.

Identification and expression of cytochrome P450 genes in the Chinese giant salamander Andrias davidianus

Cytochrome P450 (cyp) genes play vital roles in biological processes, including in metabolism of endogenous and exogenous compounds. Exogenous hormone influences on gene expression that leads to disruption of gonad development have been studied in several species, but whether exogenous hormones affect cyp genes that show sexually dimorphic expression remains to be determined. Here, we identified and characterized cyp genes from the widely-cultured Chinese giant salamander Andrias davidianus. We obtained 20 cyp genes including 11 genes with complete sequences. Phylogenetic analyses supported the classification of cyp genes similar to other vertebrates. Expression profile of female and male salamanders showed multiple cyp genes to exhibit higher expression in ovary than in testis, including cyp26a, cyp19a, cyp1a1, cyp4v2, cyp3a24, cyp2c20, cyp2d14, cyp2d15, and cyp4b; while cyp11a, cyp2b11, cyp11b1, cyp4f22, cyp2j6, cyp2k1, cyp2k4, cyp1a5 was higher in testis than in ovary. Seven sex-biased genes were detected after aromatase inhibitor injection and with exposure to high water temperatures. Cyp2k1, cyp11b1, and cyp2j6 expression were increased, while cyp26a, cyp2c20, cyp4b genes were decreased with aromatase inhibition. In ovary, cyp26a and cyp2c20 expression were significantly reduced; whereas cyp2k1, cyp2j6, and cyp2k4 expression were significantly elevated with no changes in cyp11a and cyp11b1 expression after temperature treatment. These findings provide valuable information for further study of sex differentiation mechanisms and cyp gene evolution.

Potential contributions of heat shock proteins and related genes in sexual differentiation in yellow catfish (Pelteobagrus fulvidraco)

Sex determination and differentiation in ectotherms are very complicated affairs and usually affected by both genetic and environmental factors. Because of their temperature-sensitive expression, heat shock proteins (HSPs) are good candidates for temperature-dependent sex determination (TSD). Similar to most thermosensitive fish species, the male to female ratio increases with temperature in yellow catfish (Pelteobagrus fulvidraco). Yellow catfish is also a type of sexual size dimorphic fish, and the male individuals grow much faster than females of the same age. Therefore, research of sex differentiation in yellow catfish is important in aquiculture. In this attempt, a total of seven HSPs and related genes were identified from transcriptomes of yellow catfish by 454 pyrosequencing and Solexa sequencing that we did previously, including five genes with complete open reading frame (ORF). Phylogenetically, all these genes were compared with their counterparts from other vertebrates. All these genes were sex-biased expressed in gonads. Hspa5, Hip, and Cdc37 were expressed more highly in ovary than in testis, whereas Hsp90α, Hspb2, Hspb8, and Hspbp1 were expressed more highly in testis than in ovary. Additionally, the expression of these genes was assessed after 17α-methyltestosterone (MT) and 17α-ethinylestradiol (EE2) treatment, respectively. Our result showed that working as co-chaperones, these HSPs and related genes may regulate sex steroid receptor activities to influence gonad development in yellow catfish. Our work would help in the understanding of the mechanism of sexual differentiation in teleosts.

Sex biased expression of ghrelin and GHSR associated with sexual size dimorphism in yellow catfish

Sexual size dimorphism has been observed in many cultivable fish species including yellow catfish, in which male fish grow much faster than female fish. Ghrelin is a potent stimulator of pituitary growth hormone (GH) release and known to potentially promote food intake and body weight gain. In order to investigate the molecular mechanism of sexual size dimorphism in yellow catfish (Pelteobagrus fulvidraco), ghrelin and its functional receptor, growth hormone secretagogue receptor (GHSR) cDNAs were cloned. Real-time PCR indicated that both ghrelin and GHSR were more highly expressed in hypothalamus and gut of male fish than female. During normal larval development, expression of ghrelin and GHSR genes was significantly higher in males than in females. 17a-Methyltestosterone (MT) treatment enhanced the expression of ghrelin in female larval fish and GHSR in both sexes, whereas the expression of ghrelin in male larval fish increased in the beginning, then decreased as the treatment time prolonged. Furthermore, the expression of ghrelin and GHSR in male juvenile was significantly increased compared with female juvenile, in short and long term fasting periods, suggesting that male fish may have a better appetite than female during fasting. Our results demonstrate that sex difference in the expression of ghrelin and GHSR may be involved in sexual size dimorphism by regulating feeding and GH/IGF signaling in yellow catfish.

Comparative Transcriptome Analysis of Differentially Expressed Genes and Signaling Pathways between XY and YY Testis in Yellow Catfish

YY super-males have rarely been detected in nature and only been artificially created in some fish species including tilapia and yellow catfish (Pelteobagrusfulvidraco), which provides a promising model for testis development and spermatogenesis. In our previous study, significant differences in morphology and miRNA expression were detected between XY and YY testis of yellow catfish. Here, solexa sequencing technology was further performed to compare mRNA expression between XY and YY testis. Compared with unigenes expressed in XY testis, 1146 and 1235 unigenes have significantly higher and lower expression in YY testis, respectively. 605 differentially expressed unigenes were annotated to 1604 GO terms with 319 and 286 genes having relative higher expression in XY and YY testis. KEGG analysis suggested different levels of PI3K-AKT and G protein-coupled receptor (GPCR) signaling pathways between XY and YY testis. Down-regulation of miR-141/429 in YY testis was speculated to promote testis development and maturation, and several factors in PI3K-AKT and GPCR signaling pathways were found as predicted targets of miR-141/429, several of which were confirmed by dual-luciferase reporter assays. Our study provides a comparative transcriptome analysis between XY and YY testis, and reveals interactions between miRNAs and their target genes that are possibly involved in regulating testis development and spermatogenesis.